Carpetweed family (Molluginaceae)
Description: This adventive annual plant is prostrate, branching at the base and forming a more or less circular mat about 6" high or less. The stems are glabrous and either round or angular, occasionally forming side stems. There are whorls of 3-8 leaves at intervals along the stems. These leaves are up to 1½" long and ¼" across. They are linear or narrowly oblanceolate, smooth along the margin, and hairless.
From the axils of the leaves, there are small whorls or clusters of 2-5 flowers. Each flower is about ¼" across, consisting of 5 petal-like sepals, no petals, 3-5 white stamens, and a large green ovary with a tiny tripartite style on top. The sepals are white or greenish white, often with pale green lines. The stamens are usually appressed against the walls of the ovary. The blooming period occurs from mid-summer through the fall, and lasts about 2 months. There is no noticeable floral scent. Each flower matures into a 3-valved seed capsule. Each valve of the capsule contains numerous small seeds that are reddish brown, shiny, and reniform. There are small ridges along the sides of the seeds, but they are hard to see without a magnifying glass. The root system consists of a taproot. This plant spreads by reseeding itself, and often forms colonies.
Cultivation: This plant is typically found in full or partial sun, mesic to dry conditions, and sandy soil, although it can occur in other kinds of soil as well. Open disturbed sites are preferred because it is not competitive with taller vegetation.
Range & Habitat: Carpetweed is a fairly common plant that occurs in most counties in Illinois. Habitats include lawns and gardens, construction sites, fields, areas along roadsides and railroads (including the ballast), disturbed sandy meadows, and waste areas. This species is adventive from tropical America.
Faunal Associations: The nectar and pollen of the flowers attract Halictid bees and various flies, including Syrphid flies, flesh flies, and Muscid flies. Otherwise, there is little information available about floral-faunal relationships for this species in Illinois and adjacent areas. In the desert southwest, foliage and seeds of a carpetweed species are sometimes eaten by small rodents, including kangaroo rats.
Photographic Location: Recently disturbed soil at a construction site in Meadowbrook Park, Urbana, Illinois.
Comments: Sometimes Carpetweed is classified in the Aizoaceae, rather than Molluginaceae. This is one of the few species of prostrate plants with whorled leaves and flowers, which makes this species fairly easy to identify. While the Galium spp. (Bedstraws) are sprawling plants with whorled leaves, the corollas of their flowers have 4 lobes, rather than 5. Each flower of the Bedstraws has a pair of round ovaries that lie underneath the corolla, while each flower of Carpetweed has a single oval-shaped ovary that projects above the petal-like sepals. Carpetweed is glabrous throughout, while the Bedstraws often (but not always) have clinging hairs on their foliage and seed capsules.